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Fluid flux melting generated postcollisional high Sr/Y copper ore–forming water-rich magmas in Tibet

2015; Geological Society of America; Volume: 43; Issue: 7 Linguagem: Inglês

10.1130/g36734.1

1943-2682

Yongjun Lu, Robert R. Loucks, Marco L. Fiorentini, Zhiming Yang, Zengqian Hou,

earthquake and tectonic studies

Research Article| July 01, 2015 Fluid flux melting generated postcollisional high Sr/Y copper ore–forming water-rich magmas in Tibet Yong-Jun Lu; Yong-Jun Lu 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Robert R. Loucks; Robert R. Loucks 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Marco L. Fiorentini; Marco L. Fiorentini 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Zhi-Ming Yang; Zhi-Ming Yang 2Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Search for other works by this author on: GSW Google Scholar Zeng-Qian Hou Zeng-Qian Hou 2Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Search for other works by this author on: GSW Google Scholar Author and Article Information Yong-Jun Lu 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Robert R. Loucks 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Marco L. Fiorentini 1Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia Zhi-Ming Yang 2Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Zeng-Qian Hou 2Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Publisher: Geological Society of America Received: 25 Feb 2015 Revision Received: 16 Apr 2015 Accepted: 18 Apr 2015 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (7): 583–586. https://doi.org/10.1130/G36734.1 Article history Received: 25 Feb 2015 Revision Received: 16 Apr 2015 Accepted: 18 Apr 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Yong-Jun Lu, Robert R. Loucks, Marco L. Fiorentini, Zhi-Ming Yang, Zeng-Qian Hou; Fluid flux melting generated postcollisional high Sr/Y copper ore–forming water-rich magmas in Tibet. Geology 2015;; 43 (7): 583–586. doi: https://doi.org/10.1130/G36734.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Miocene postcollisional porphyry Cu deposits in southern Tibet are genetically associated with dacitic-rhyolitic intrusions with unusually high Sr/Y ratios (>40), which have been attributed to dehydration melting of garnet amphibolite in a thickened lower crust. To test this hypothesis and examine the hydration state of copper ore–forming high Sr/Y magmas, we utilize a geohygrometer for granitoid rocks, entailing zircon-saturation thermometry and H2O-dependent phase equilibria. The results show that these Tibetan high Sr/Y magmas had dissolved H2O contents >10 wt%, which considerably exceeds the water supply by dehydration melting of basaltic amphibolites (maximum of 6.7 ± 1.4 wt%). Our results indicate that high Sr/Y dacitic-rhyolitic magmas cannot be produced by dehydration melting of basaltic amphibolites. While H2O-added melting of basaltic amphibolites can produce high Sr/Y dacitic-rhyolitic melts, it does not yield high enough Mg# (>50) to match the Tibetan ore-forming porphyries. We propose an alternative model for the genesis of copper ore–forming high Sr/Y magmas in Tibet, and suggest that the high Sr/Y dacitic-rhyolitic porphyries in southern Tibet are residually H2O-enriched, high-pressure differentiation products of hydrous mafic partial melts of Tibetan mantle. This hypothesis is based on the previous investigation of Miocene mafic microgranular enclaves (mantle-derived melts), which define a fractionation trend with, and have Sr-Nd-Hf isotopic compositions similar to, the host Tibetan ore-forming porphyries. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.